1. Field of the Invention
The present invention relates to a substrate cleaning apparatus used in the manufacturing of a semiconductor device, and, more particularly, to an apparatus for cleaning substrates (wafers) arranged vertically.
2. Description of the Related Art
In the manufacturing of semiconductor devices, for example, each semiconductor wafer is washed repeatedly in the course of the various manufacturing steps, since the wafer surface, if contaminated, will adversely affect the characteristics of the finished semiconductor devices. Hence, thorough cleaning of the wafers is an important part of the manufacturing of semiconductor devices.
As an apparatus for cleaning a to-be-treated semiconductor wafer substrate, a batch type cleaning apparatus has been so far employed, which is adapted to wash a plurality of substrates at a time. This type of apparatus is disclosed in Japanese Patent Disclosure (KOKAI) 52-95166. In order to obtain a high yield in the manufacturing process of semiconductor devices of high integration density, such as 4M and 16M devices, and microminiaturized circuit patterns, increasingly strict demands have been made in regard to the thoroughness of the cleaning process. However, the aforementioned batch type substrate cleaning apparatus cannot meet the currently required standards, for a variety of reasons, the such principal reason being its inability to wash every substrate to the same degree of thoroughness.
Recently, a sheet-by-sheet type cleaning apparatus has been developed which is designed to wash to-be-treated substrates one sheet at a time. This type of cleaning apparatus includes a plurality of narrow-profile treatment chambers which are arranged sequentially in a parallel array along a path on which a carrier is run to transfer the substrate to the treatment chamber. Specifically, the substrate is held by a suction arm of the carrier and is transferred by that arm from one treatment chamber to another. The substrate is inserted horizontally into the respective treatment chamber and washed while in this state.
Since, in this case, the length of the apparatus corresponds at least to the length of one treatment chamber x the number of chambers, the apparatus becomes undesirably bulky. If the apparatus is designed to wash, for example, an 8-inch substrate, then the length of one treatment chamber would be ten and a few inches. Assuming that there are three chambers of this size, in addition to a cassette loader and an unloader, then the length of the cleaning apparatus would come to at least 5 feet. Generally, the cleaning apparatus is installed within a clean room whose construction and maintenance costs are high. It is therefore desirable that the amount of space taken up by the cleaning apparatus be as small as possible.
In this type of cleaning apparatus, the substrate is washed often, with an ultrasound oscillation being simultaneously applied thereto. In this case, however, an oscillation source is provided only on the rear side of the substrate, failing to effectively wash away a contaminant which is physically deposited on the major surface of the substrate.
Furthermore, when the substrate is immersed in the cleaning solution, a buoyant force is exerted on the substrate in a cross sectional direction and due care has to be exercised in the design of the cleaning apparatus not to apply any excessive load to that thin substrate upon the immersion of the substrate into the cleaning solution.